PAT (Advanced) 1069. The Black Hole of Numbers (20)

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

int make_big(int n)
{
	int ary[4];
	ary[0] = n / 1000;
	ary[1] = n / 100 % 10;
	ary[2] = n / 10 % 10;
	ary[3] = n % 10;
	sort(ary, ary + 4);
	int result = 0;
	for (int i = 3; i >= 0; i--)
	{
		result *= 10;
		result += ary[i];
	}
	return result;
}

int make_small(int n)
{
	int ary[4];
	ary[0] = n / 1000;
	ary[1] = n / 100 % 10;
	ary[2] = n / 10 % 10;
	ary[3] = n % 10;
	sort(ary, ary + 4);
	int result = 0;
	for (int i = 0; i < 4; i++)
	{
		result *= 10;
		result += ary[i];
	}
	return result;
}
int main()
{
	int n;
	cin >> n;
	int big = make_big(n);
	int small = make_small(n);
	if (big == small)
	{
		printf("%04d - %04d = 0000\n", big, small);
	}
	else
	{
		while (big - small != 6174)
		{
			int result = big - small;
			printf("%04d - %04d = %04d\n", big, small, result);
			big = make_big(result);
			small = make_small(result);
		}
		printf("%04d - %04d = 6174\n", big, small);
	}
}